Modern vehicles and particularly automobiles, mostly so-called SUVs, are provided with external view cameras to enhance the driver's vision and to improve safety. These integrated video cameras generate an image for display to the driver, operator or to other occupants or users within the vehicle's interior. Sensors in the sense of the present application are for instance such sensors in passenger cars which detect approaching and passing cars from behind and which are not visible to the driver in the rear mirrors due to the blind angle not covered by the rear view mirrors.
Rear view cameras which are often integrated into the rear bumper, the hatch or the luggage compartment door of the vehicle nearby the licence plate are normally utilized to generate a lane departure warning signal to the driver or to detect objects behind the vehicle which are normally not visible in the rear view mirror. Rear view cameras in particular for detecting the correct parking position in SUV's therefore have become quite popular.
Camera lenses or protective lens covers however, are exposed to the vehicle's surroundings and dirt and debris, mud, salt spray, etc., accumulates on the lens or a lens cover during operation of the vehicle. Particularly, if cameras and/or sensors are integrated in the rear bumper or in the luggage compartment door of the vehicle, they are particularly exposed to dirt and mud spray.
It is therefore generally known to provide external lens washing systems for cleaning lenses and sensors.
For example WO 2012/138455 A1 discloses an external lens washing system which has an aiming fixture configured to support and constrain an external lens which is exposed to the elements and susceptible to become soiled with debris. The lens washing system comprises a nozzle assembly aimed towards the external lens, having at least one laterally offset washing nozzle projecting from the aiming fixture to spray washing fluid towards the external lens surface, spraying at a shallow, glancing spray aiming angle to impinge upon and wash the lens external surface. The washing system nozzle is integrated into the camera housing and the nozzles of the washing systems are configured to generate an oscillating spray to clean the exterior objective lens surface.
Some external camera systems include convex or dome shaped lens surfaces which require specific liquid spray patterns in order to achieve a satisfying cleaning effect. This issue is already addressed in WO 2012/138455 A1 and, as a solution to this issue, it is proposed to provide fluid oscillators as cleaning fluid nozzles.
There is, however, another issue which such dome shaped lenses or lens covers, i.e., small droplets of rain or cleaning fluid adhere to the lens cover and also deteriorate the visual image displayed for instance in the navigation system of the vehicle. In order to overcome this drawback in WO 2012/138455 A1 it is proposed to provide a cover, the exterior surface of which is coated with an anti wetting property such as via a hydrophilic coating.
Such coating however has the drawback that it is susceptible to wear and that the effects of the coating are not always fully satisfying.
Another approach for keeping optical lenses on motor vehicles clean is for instance disclosed in WO 01/68425 A1. According to the teaching of this reference a transparent cover of the optical element is treated with a directed gas, in particular, an air stream, such that on moving the cover relative to the environment, no ambient atmosphere, in particular ambient air reaches the surface of the cover. In one embodiment, compressed air is blown through a nozzle, by means of which a transversal air flow is generated. This approach aims to avoid any build up of debris during operation of the vehicle right from the beginning so that eventual cleaning cycles may be minimized. A drawback of this system is that for generating a transversal air flow a constantly driven compressor is required.
Yet another cleaning concept is disclosed in WO 02/072274 A1. This publication proposes fluid and air nozzle assemblies which are capable of propelling streams of a cleaning fluid and an air mixture onto a vehicle vision device, visible indicator, or sensor. These nozzle assemblies are mounted on a vehicle adjacent to the vehicle vision device and are positioned such that liquid from one type of nozzle and air jets from another type of nozzle intersect prior to impinging upon the vehicle vision device in order to form a spray mixture that cleans the exposed surface of the vehicles vision device.
A similar concept is disclosed in D 10 2010 022 163 A1. This reference discloses a device for keeping an optical element as for instance a camera lens clean during operation of the vehicle also by generating a transversal air flow. This air flow, however, is not generated by a compressor but rather by a so called wind trap which is a passive fluid dynamical device. The known devices and methods nevertheless suffer from the drawback that they either are not effective or are relatively complex and costly.